This invention relates to a method of using polydodecenamers as reinforcing resins for elastomers. In a compositional aspect, this invention relates to elastomers compounded with polydodecenamer reinforcing resins.
Reinforcing resins are customarily added to elastomers prior to vulcanization, primarily to increase the hardness of the vulcanizates. Styrene-butadiene copolymers having a high styrene content are recognized in the art as suitable resins for this purpose.
Recently, difficulties have been encountered, due to a worldwide shortage of aromatics, in obtaining styrene monomer required for all previously applicable purposes. Consequently, there is an urgent need for styrene-free substitute products, such as reinforcing resins based on styrene.
Moreover, the styrene-rich reinforcing resins have disadvantages which limit their field of use. On the one hand, the elastomers which are combined with such reinforcing resins have impaired properties after vulcanization with respect to dynamic stress, as manifested, for example, by reduced elasticity and higher internal heat buildup. On the other hand, reinforcing resins having a high styrene content are not entirely suitable for addition to the inexpensive polyolefin rubbers, e.g., ethylene-propylenediene rubber, since they generally cause impairment of a number of properties controlling the use of the products.
French Pat. No. 2,157,214 discloses adding polyolefins to the elastomers as reinforcing resins. Although the hardness of the vulcanizates can thereby be increased, such a step simultaneously results in a great reduction in strength and of the utilitarian properties connected therewith, because the polyolefins are not incorporated into the vulcanizate structure.
Thus, there is a continuing need for resins having none of the disadvantages of reinforcing resins of the prior art as well as for styrene-free reinforcing resins.
The results attained using polydodecenamer reinforcing resins are unexpected in view of known uses of polyalkenamers.
German Unexamined Laid-Open Application DOS 1,595,739 discloses that polyoctenamers having a trans-vinylene content below about 60% are rubbery and are suitable for the production of a plurality of rubber products. Those having trans-vinylene contents of about 25-50%, and preferably below 25%, are recommended for use in tires.
Polyoctenamers having a trans-vinylene content of 60-70% have a high impact resistance and are used in jackets for golf balls and sheathings for cables, but polyoctenamers having a trans-vinylene content above 75% are described as fibrous and crystalline and are suitable for use in molded products.
According to DOS 2,123,452, a favorable effect is achieved with regard to green tensile strength, building tack, stretchability, aging characteristics, and degradation behavior, by adding polypentamers having a trans-vinylene content of more than 30% of polyisoprene in amounts of 5-95% by weight of the total mixture. Similar assertions are made with respect to building tack in DOS 2,063,716 for mixtures of polypentenamer and ethylene-propylene-diene elastomer (EPDM).
Finally, it is known from DOS 2,131,354 corresponding to U.S. Pat. 3,816,358 that adding 2-20% by weight of polyoctenamer and/or polydodedenamer with trans-vinylene contents of above 60% and RSV values of 0.2 - 3.0 dl./g. to an elastomeric compound increases the green tensile strength and the thermoplasticity of the unvulcanized rubber mixture, without a marked effect on the properties of the finished vulcanizate.
None of the above teachings suggests the use of specific polydodecenamers as reinforcing resins for elastomers. It is also surprising, in view of the art cited above, that polydodecenamers used in accordance with this invention can replace the styrene-rich reinforcing resins and provide improved properties to the product in their practical utilities and a wider field of application.